Vertical take-off and landing aircraft

ABSTRACT

Disclosed herein is a vertical take-off and landing (VTOL) aircraft having three lifting surfaces and separate lift and cruise systems. The VTOL aircraft may include a fuselage having a roll axis, a thrust rotor to produce a propulsion thrust, first and second rotor booms, first and second canard surfaces, first and second wing surfaces, first and second tail surfaces, and a plurality of lift rotors to produce a lifting thrust force. The plurality of lift rotors includes a first plurality of lift rotors positioned on the first rotor boom and a second plurality of lift rotors positioned on the second rotor boom. The first and second rotor booms may be substantially parallel to the roll axis of the fuselage, where the fuselage is positioned between the first and second rotor booms. Each of the first and second rotor booms may be secured to the aircraft at three locations.

TECHNICAL FIELD

The present invention relates to a vertical take-off and landing (VTOL)aircraft, more specifically, to a VTOL aircraft with significant range,even more specifically to a VTOL aircraft having three lifting surfacesand separate lift and propulsion systems.

BACKGROUND

VTOL aircraft typically fall into one of three different propulsionsystem categories. The first category employs a joined lift-plus-cruisepropulsion system, which suffers from limited range due toinefficiencies in producing powered lift. A second category employs atilting mechanism to turn (redirect) the force produced by the rotorsfrom lift to cruise thrust once at a predetermined altitude. Thisconcept, however, relies on a complex tilting mechanism that is heavy,introduces a failure path, and is costly to build and maintain.

A third category employs a series of rotors, each of which isindividually dedicated to either lift or cruise thrust, where the liftrotors are only active during vertical takeoff and landing and thecruise rotor(s) are only active during the cruise portion of flight. Forexample, U.S. Pat. No. 8,393,564 B2 to Kroo, tilted “Personal Aircraft,”describes an aircraft configuration that uses a combination of multiplevertical lift rotors, tandem wings, and forward thrust propellers. Inaddition, U.S. Pat. Pub. No. 2016/0236774 to Hans Niedzballa, titled“Aircraft Capable of Vertical Takeoff,” describes an aircraft with abearing structure having a central fuselage and two pylons each situatedat a distance laterally from the fuselage. Attached to the bearingstructure of the aircraft are hub rotors to provide an upward driveforce acting in the vertical direction, and a thrust drive to providethrust force acting in the horizontal direction.

Existing VTOL aircraft, such as the VTOL aircraft described byNiedzballa, suffers from a number of limitations. For example,significant vibration during transition flight is generated when asingle attachment point is used between each rotor boom and thefuselage. In addition, constraining the rotor blades to the dimensionsof the pylon imposes limitations on the number of rotors that may beemployed in a given aircraft. Finally, in addition to added weight,cost, and complexity, stowing rotors within the rotor booms behind acloseable door does not appreciably reduce drag, can increase noisedramatically, and decreases rotor efficiency.

In view of the foregoing, a need exist for a VTOL aircraft withsignificant range, decreased noise, and increased efficiency.

SUMMARY OF THE INVENTION

The present invention is directed to a VTOL aircraft with significantrange, decreased noise, and increased efficiency.

According to one aspect, a vertical take-off and landing (VTOL) aircraftcomprises: a fuselage having a roll axis; a thrust rotor to produce apropulsion thrust; first and second rotor booms, wherein the first andsecond rotor booms are substantially parallel to the roll axis of thefuselage, and the fuselage is positioned between the first and secondrotor booms; first and second canard surfaces, each of said first andsecond canard surfaces having a canard proximal end and a canard distalend, wherein the canard proximal end of the first canard surface iscoupled to the fuselage and the canard distal end of the first canardsurface is coupled to the first rotor boom, wherein the canard proximalend of the second canard surface is coupled to the fuselage and thecanard distal end of the second canard surface is coupled to the secondrotor boom; first and second wing surfaces, each of said first andsecond wing surfaces having a wing proximal end and a wing distal end,wherein the wing proximal end of each of the first wing surface andsecond wing surface is coupled to the fuselage, wherein the first wingsurface is coupled to the first rotor boom and the second wing surfaceis coupled to the second rotor boom; first and second tail surfaces,each of said first and second tail surfaces having a tail proximal endand a tail distal end, wherein the tail proximal end of the first tailsurface is coupled to the fuselage and the tail distal end of the firsttail surface is coupled to the first rotor boom, wherein the tailproximal end of the second tail surface is coupled to the fuselage andthe tail distal end of the second tail surface is coupled to the secondrotor boom; a first plurality of lift rotors positioned on the firstrotor boom to produce a first lifting thrust force; and a secondplurality of lift rotors positioned on the second rotor boom to producea second lifting thrust force.

In certain aspects, a cross-member structure may be coupled to each ofsaid first and second rotor booms, wherein the cross-member structure issubstantially perpendicular to the said first and second rotor booms.

In certain aspects, the cross-member structure is positioned aft of saidfirst and second wing surfaces.

In certain aspects, the tail distal end of the first tail surface iscoupled to the first rotor boom via a cross-member structure, and thetail distal end of the second tail surface is coupled to the secondrotor boom via the cross-member structure.

In certain aspects, the cross-member structure is a horizontalstabilizer.

In certain aspects, each of said first rotor boom comprises a firstvertical stabilizer and said second rotor boom comprises a secondvertical stabilizer.

In certain aspects, the first vertical stabilizer, the second verticalstabilizer, and the horizontal stabilizer are arranged in an H-tailarrangement.

In certain aspects, the first and second tail surfaces are configured atanhedral angles to define, together with the first vertical stabilizer,the second vertical stabilizer, and the horizontal stabilizer, acombination H- and

-tail arrangement.

In certain aspects, the first and second canard surfaces and the firstand second tail surfaces are configured at anhedral angles.

In certain aspects, the first and second wing surfaces are configured atdihedral angles.

In certain aspects, each of the first plurality of lift rotors and thesecond plurality of lift rotors employs a propeller consisting of tworotor blades.

In certain aspects, the propeller is arranged with the two rotor bladesaligned fore and aft when in a stowed configuration.

In certain aspects, the propeller is automatically arranged in a stowedconfiguration during cruise flight.

In certain aspects, third and fourth rotor booms may be provided,wherein the third and fourth rotor booms are substantially parallel tothe roll axis of the fuselage and outboard relative to the first andsecond rotor booms.

In certain aspects, the third rotor boom is coupled to the first wingsurface and the fourth rotor boom is coupled to the second wing surface.

In certain aspects, the third rotor boom comprises a third plurality oflift rotors and the fourth rotor boom comprises a fourth plurality oflift rotors.

In certain aspects, the first plurality of lift rotors consists of fourlift rotors and the second plurality of lift rotors consists of fourlift rotors.

In certain aspects, the third plurality of lift rotors consists of twolift rotors and the fourth plurality of lift rotors consists of two liftrotors.

In certain aspects, each of the first and second lifting thrust forcesis directed away from the fuselage.

In certain aspects, each of the first and second plurality of liftrotors includes a propeller driven by an electric motor.

In certain aspects, the thrust rotor includes a propeller driven by anelectric motor.

In certain aspects, the thrust rotor is coupled to the fuselage.

In certain aspects, the thrust rotor is configured in a pusher propellerconfiguration.

DESCRIPTION OF THE DRAWINGS

These and other advantages of the present invention may be readilyunderstood with the reference to the following specifications andattached drawings wherein:

FIG. 1a illustrates a front perspective view of a first example VTOLaircraft.

FIG. 1b illustrates a bottom perspective view of the VTOL aircraft ofFIG. 1 a.

FIG. 1c illustrates a top plan view of the VTOL aircraft of FIG. 1 a.

FIG. 1d illustrates a bottom plan view of the VTOL aircraft of FIG. 1 a.

FIG. 1e illustrates a left side elevation view of the VTOL aircraft ofFIG. 1 a.

FIG. 1f illustrates a right side elevation view of the VTOL aircraft ofFIG. 1 a.

FIG. 1g illustrates a front elevation view of the VTOL aircraft of FIG.1 a.

FIG. 1h illustrates a rear elevation view of the VTOL aircraft of FIG. 1a.

FIG. 2 illustrates a block diagram of an example aircraft controlsystem.

FIG. 3a illustrates a top plan view of a second example VTOL aircraft.

FIG. 3b illustrates a bottom plan view of the VTOL aircraft of FIG. 3 a.

FIG. 4 illustrates a rear elevation view of the empennage with portionsof the VTOL aircraft omitted.

FIG. 5 illustrates a lift rotor stowed in an example fore and aftarrangement.

DETAILED DESCRIPTION

Preferred embodiments of the present invention may be describedhereinbelow with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail because they may obscure the invention inunnecessary detail. For this disclosure, the following terms anddefinitions shall apply.

As used herein, the words “about” and “approximately,” when used tomodify or describe a value (or range of values), mean reasonably closeto that value or range of values. Thus, the embodiments described hereinare not limited to only the recited values and ranges of values, butrather should include reasonably workable deviations.

As utilized herein, “and/or” means any one or more of the items in thelist joined by “and/or”. As an example, “x and/or y” means any elementof the three-element set {(x), (y), (x, y)}. In other words, “x and/ory” means “one or both of x and y”. As another example, “x, y, and/or z”means any element of the seven-element set {(x), (y), (z), (x, y), (x,z), (y, z), (x, y, z)}. In other words, “x, y, and/or z” means “one ormore of x, y, and z”.

The terms “aerial vehicle” and “aircraft” refer to a machine capable offlight, including, but not limited to, traditional aircraft and verticaltakeoff and landing (VTOL) aircraft.

The terms “circuits” and “circuitry” refer to physical electroniccomponents (i.e. hardware) and any software and/or firmware (“code”)which may configure the hardware, be executed by the hardware, and orotherwise be associated with the hardware. As used herein, for example,a particular processor and memory may comprise a first “circuit” whenexecuting a first set of one or more lines of code and may comprise asecond “circuit” when executing a second set of one or more lines ofcode. As utilized herein, circuitry is “operable” to perform a functionwhenever the circuitry comprises the necessary hardware and code (if anyis necessary) to perform the function, regardless of whether performanceof the function is disabled or not enabled (e.g., by anoperator-configurable setting, factory trim, etc.).

The terms “communicate” and “communicating” refer to (1) transmitting,or otherwise conveying, data from a source to a destination, and/or (2)delivering data to a communications medium, system, channel, network,device, wire, cable, fiber, circuit, and/or link to be conveyed to adestination.

The term “composite material” refers to a material comprising anadditive material and a matrix material. For example, a compositematerial may comprise a fibrous additive material (e.g., fiberglass,glass fiber (“GF”), carbon fiber (“CF”), aramid/para aramid syntheticfibers, etc.) and a matrix material (e.g., epoxies, polyimides, andalumina, including, without limitation, thermoplastic, polyester resin,polycarbonate thermoplastic, casting resin, polymer resin, acrylic,chemical resin). In certain aspects, the composite material may employ ametal, such as aluminum and titanium, to produce fiber metal laminate(FML) and glass laminate aluminum reinforced epoxy (GLARE). Further,composite materials may include hybrid composite materials, which areachieved via the addition of some complementary materials (e.g., two ormore fiber materials) to the basic fiber/epoxy matrix.

As utilized herein, the term “exemplary” means serving as a non-limitingexample, instance, or illustration. As utilized herein, the terms “e.g.”and “for example” set off lists of one or more non-limiting examples,instances, or illustrations.

A number of considerations should be taken into account when designing asmall VTOL aircraft. A first consideration is efficiency, which relatesto, and dictates, the range of the aircraft. A second consideration isnoise, which relates to the total lifting rotor disc area. As will bediscussed in detail below, an aircraft configuration with separate liftand propulsion may be employed to increase efficiency, while reducingnoise. Third, aircraft with the ability to produce both powered lift andforward thrust must be designed to operate efficiently in the transitionregion (e.g., transition flight) between vertical flight (e.g., hoverflight) and cruise flight (e.g., forward/horizontal/wing-borne flight).Finally, VTOL aircraft should be designed to ensure that the wake fromthe power lift components (e.g., lift rotors) does not interferenegatively with lifting surfaces to cause a stall condition.

The subject aircraft offers a number of advantages and providesunrivaled performance for the metrics of interest for small VTOLaircraft, such as range, reliability, and noise.

First, the VTOL aircraft offers a stiffer, lighter-weight structure. Therotor booms, which attach the lift rotors to the VTOL aircraft, aresecured to the aircraft at three locations (e.g., via canard, primary,and tail wings). This configuration eliminates the need for cantileversexhibited in other designs, which are prone to vibration and requiresignificant additional structural mass to achieve comparableperformance. Indeed, airframe stiffness is particularly important inreducing vibration in aircraft that employ rotors having a spin axisroughly perpendicular to the flight direction, which experience a highairspeed on the advancing blade (tangential speed plus flight speed) anda low airspeed on the retreating blade. In fact, the retreating bladeexhibits airflow from the trailing edge to the leading edge near thehub. Because of this airspeed disparately, more lift is generated on theadvancing blade, which results in a rolling moment into the aircraft(e.g., via the rotor boom). This cyclical rolling moment going into therotor boom (or other airframe structure) will excite vibration if thestructure is not stiff enough to resist it. Articulated hubs, such asthose used on helicopters, are designed to mitigate this rolling moment,but such articulated hubs are complex, unreliable, expensive, heavy, andcreate drag.

Second, the VTOL aircraft interleaves the rotors and lifting surfaces inthe same plane, which requires less power during transition flightbetween forward flight and hover flight. Interleaving the rotors (e.g.,lift rotors) also ensures that the wake from the rotors does notinterfere negatively with lifting surfaces (e.g., the canard, primary,and tail wings) to cause a stall condition.

Third, the VTOL aircraft provides more loading flexibility due to higheraerodynamic stability. Specifically, the VTOL aircraft employs threelifting surfaces (canard, primary, and tail wing) to produce a broadrange of stable center of gravity positions. This range allows forhighly variable loading configurations, reducing the need to balancepassenger and cargo weight. As will be shown, the three lifting surfacesconnect the fuselage to the rotor booms to form a uniform structure.Finally, the VTOL aircraft enables application of a larger disc area,which reduces hover power and energy requirements and provides betternoise performance.

FIGS. 1a through 1h illustrate an exemplary VTOL aircraft 100 withseparate lift and forward propulsion systems. As illustrated, the VTOLaircraft 100 generally comprises an upper airframe portion 100 a that iscoupled to a lower airframe portion 100 b. In certain aspects, the upperairframe portion 100 a may be removably coupled with the lower airframeportion 100 b to more easily enable repair or replacement of eitherairframe structure, or portion thereof.

Employing separate lift and forward propulsion systems reducescomplexity, increases redundancy, and exploits the lift productionefficiencies of the primary wings 106. It also allows for the lift andforward propulsion systems to be separately optimized for a specifictask, thereby eliminating the requirement for variable pitch rotorblades. As illustrated, the VTOL aircraft 100 employs a forwardpropulsion system having one or more thrust rotors 110 (i.e., horizontalthrust rotors) to produce a propulsion thrust force acting in thehorizontal direction, and a lift system comprising a plurality of liftrotors 124 (i.e., vertical thrust rotors) to produce a lifting thrustforce acting in the vertical direction.

The structural components of the VTOL aircraft 100 may be fabricatedusing materials that are lightweight, with a high specific strength,heat resistant, fatigue load resistant, crack resistant, and/orcorrosion resistant. Suitable materials include, for example, compositematerials and metals (e.g., aluminum, steel, titanium, and metalalloys). The size and purpose of the VTOL aircraft 100 may dictate thetype of materials used. For instance, smaller to midsize aircraft may bemore easily fabricated from composite materials, while larger aircraftmay warrant metal. Indeed, the internal airframe structure may be ametal, while the body panels (skin) may be fabricated from compositematerial and/or metal. Metal fittings may be further used to couple orjoin the various components of the VTOL aircraft 100, whether metal orcomposite material.

While separate terms are used in the written description to describe theupper airframe portion 100 a, the lower airframe portion 100 b, and thecomponents thereof, the various functions to be performed do notnecessarily have to be performed by separate physical structures. Thatis, functions of the upper airframe portion 100 a and functions of thelower airframe portion 100 b can be performed by different structuralcomponents of the VTOL aircraft 100, or also by the same structuralcomponents of the VTOL aircraft 100. For example, the canard surfaces104 and tail surfaces 108, which will be described as part of the upperairframe portion 100 a, are used, at least in part, to mechanicallycouple the upper airframe portion 100 a to the lower airframe portion100 b and, therefore, may be formed as integral with either or both ofthe upper and the lower airframe portions 100 a, 100 b. Similarly, thecanard surfaces 104 and tail surfaces 108 may be separate from each ofthe upper and the lower airframe portions 100 a, 100 b. Additionally,other structures (e.g., the outer skin of the aircraft) may be sharedacross multiple structures within the aircraft.

Upper Airframe Portion 100 a.

The upper airframe portion 100 a generally comprises a fuselage 102, aset of canard surfaces 104 (together defining a canard wing set), a setof primary wings 106 (together defining a primary wing set), a set oftail surfaces 108 (together defining a tail wing set), and at least onethrust rotor 110 to produce thrust with a force vector acting in thehorizontal direction.

Fuselage 102.

The fuselage 102 may be a monocoque structure or a semi-monocoquestructure, which employs a hybrid combination of tensile stressed skinand a compressive structure made up of longerons and ribs or frames. Asillustrated, the fuselage 102 can include a cockpit/cabin 114 for one ormore human operators and/or passengers. For example, the illustratedVTOL aircraft 100 is configured to carry 1 to 4 passengers (e.g., about180 to 750 pounds), plus cargo. The VTOL aircraft 100 may be used as,for example, an air taxi, emergency vehicle (e.g., ambulance), pleasurecraft, cargo transport, etc.

The cockpit/cabin 114 may include a forward facing transparent aircraftcanopy 134 fabricated from, for example, a glass material, and/or anacrylic material. In certain aspects, however, the aircraft canopy 134may be configured to provide a substantially unobstructed view to thepassengers/pilot (e.g., a 360-degree view to provide forward, rear,side, and upward views). The VTOL aircraft 100 is generally described ashaving a cockpit for manned operation, but may also be configured asunmanned (i.e., requiring no onboard pilot) or as both unmanned andfully autonomous (i.e., requiring neither an onboard pilot nor a remotecontrol pilot). For example, the VTOL aircraft 100 may be remotelycontrolled over a wireless communication link by a human operator,computer operator (e.g., remote autopilot), or base station.

The fuselage 102 may further include one or more avionics bays 136 tohouse cargo, sensors, control systems, etc. While the VTOL aircraft 100is illustrated as having a fuselage 102 designed to carry passengers, itis contemplated that other airframe structures may be employed tofacilitate a particular need or purpose. If the VTOL aircraft 100 isfully autonomous, for example, the airframe structure may be designed tocarry only cargo and, to that end, may be sized and shaped to optimizecargo hauling and may further omit passenger centric features, such asthe transparent canopy.

Aircraft Control System 200.

An example aircraft control system 200 is illustrated in FIG. 2. Theaircraft control system 200 is configured to control the variousaircraft components and functions. To that end, the aircraft controlsystem 200 may include a processor 202, a navigation system 204, asurveillance payload 206, a data storage device 208, a flight controller210, a battery system 212 (or other power/fuel source), and acommunication interface 214. The one or more processors 202 may beconfigured to perform one or more operations based at least in part oninstructions (e.g., software) stored to the onboard data storage device208 (e.g., hard drive, flash memory, or the like). The aircraft controlsystem 200 may further include other desired services, such as awireless communication device (e.g., via the communication interface214).

The navigation system 204 may include an Inertial Navigation System(“INS”) 204 a that is communicatively coupled with a global positioningsystem (GPS) 204 b and/or an inertial measurement unit (IMU) 204 c. TheGPS gives an absolute drift-free position value that can be used toreset the INS solution or can be blended with it by use of amathematical algorithm, such as a Kalman Filter. The intelligence,surveillance, and reconnaissance (“ISR”) surveillance payload 206 may beused to collect data and/or monitor an area using a camera 206 a orother device 206 b.

The flight controller 210 may be operatively coupled to the processor202 to control operation of the various actuators 210 a (e.g., those tocontrol movement of flight surfaces) and/or thrusters 210 b (e.g., thethrust rotors 110 and the lift rotors 124) in response to commands froman operator, autopilot, or other high-level system via the communicationinterface 214. In operation, the flight controller 210 may dynamically(and independently) adjust thrust from each of the lift rotors 124 oneach rotor boom 118 during the various stages of flight (e.g., take-off,cruising, landing) to control roll, pitch, or yaw of the VTOL aircraft100. In other words, the flight controller 210 can independently controleach of the lift rotors 124 on a given rotor boom 118 to generate adesired lift thrust for each of the lift rotors 124. For example, whenrotors with rotor blades (e.g., propellers) are used, the flightcontroller 210 may vary the RPM of the rotor and/or, where desired, varythe pitch of the rotor blade. When a wet engine (e.g., gas turbineengine) is used, thrust may be adjusted by controlling (e.g.,increasing/decreasing) the fuel flow to the combustion chamber, while anelectric motor may be controlled by adjusting power supplied to eachelectric motor from a battery system 212. The battery system 212 mayinclude a battery bank 212 a and a battery controller 212 b to managepower flow to aircraft components (e.g., lift rotors 124) or betweenbattery cells within the battery bank 212 a. As explained below, theVTOL aircraft 100 may be all-electric aircraft, hybrid, etc. The flightcontroller 210 may also dynamically and independently adjust thrust fromeach rotor to increase efficiency during transition. An example controlsystem for operating multiple rotors (e.g., lift-fans) during transitionis described by commonly owned U.S. Pat. Pub. No. 2016/0144956 to RobertParks, entitled “System and Method for Improving Transition Lift-FanPerformance.”

Three Lifting Surfaces.

The three lifting surface design creates a large range of viable centerof gravity locations, opening the space of loading configurations toallow for variations in number, weight, and distribution of passengersand cargo. Each of the lifting surfaces—flight surfaces, such as thecanard surfaces 104, the primary wings 106, and tail surfaces 108—may becoupled to (or integrated with), via their proximal ends, the fuselage102. The illustrated three-surface design increases the aerodynamicstability margin, allowing for a greater range of loading configurationsfor lift rotors 124.

During cruise flight, the canard surfaces 104, the primary wings 106,and tail surfaces 108 provide lift to the VTOL aircraft 100 via theirairfoil shape. As illustrated, the primary wings 106 may be configuredat a dihedral angle (an upward angle from horizontal), while the canardsurfaces 104 and tail surfaces 108 may be configured at an anhedralangle (a negative dihedral angle—downward angle from horizontal). Inother words, the primary wings 106 may be configured in a “V”configuration, while the canard surfaces 104 and tail surfaces 108 maybe shaped like in an inverted V configuration (i.e., “

” configuration). The primary wings 106 are illustrated as forward-sweptwings to allow for the center of gravity (COG) placement to be closer toaerodynamic center; however, other configurations are contemplated, suchas back-swept, tapered, rectangular, elliptical, forward-swept, and thelike.

As illustrated, each of the canard surfaces 104, the primary wings 106,and tail surfaces 108 is interleaved to avoid the rotor wake from thelift rotors 124. In other words, when viewed from above (e.g., asillustrated in FIG. 1c ), one of the three lifting surfaces 104, 106,108 is positioned (e.g., coupled, directly or indirectly, to the rotorboom 118) at a point between each of the four lift rotors 124 tomitigate the rotor wake. Specifically, FIG. 1c illustrates where,starting at the forward end (nose end) of the rotor boom 118, the threelifting surfaces 104, 106, 108 and four lift rotors 124 are interleavedin a non-overlapping arrangement such that there is: a first lift rotor124, the canard surface 104, a second lift rotor 124, the primary wing106 (which may be coupled to the rotor boom 118 via a wing supportstructure 130), a third lift rotor 124, the tail surface 108 (which maybe coupled to the rotor boom 118 via a horizontal stabilizer 122), andfinally, a fourth lift rotor 124. In addition to lift, the three liftingsurfaces 104, 106, 108 provide rigidity to the VTOL aircraft 100 bycoupling the upper and the lower airframe portions 100 a, 100 b. Asillustrated, the distal end of each primary wing 106 extends upward andbeyond the dimensions of the lower airframe portion 100 b, while thedistal ends of the canard surfaces 104 and tail surfaces 108 extenddownward and terminate at (and couple to) the lower airframe portion 100b. The distal end of each primary wing 106 may include a winglet 116 tofurther improve the efficiency of the VTOL aircraft 100.

Each of the canard surfaces 104, the primary wings 106, and tailsurfaces 108 may further comprise one of more control surfaces. Asillustrated, each primary wing 106 may, for example, include one or moretrailing edge flaps 112 and/or trim tabs. While only the primary wings106 are illustrated as having control surfaces, it is contemplated thatthe canard surfaces 104 and tail surfaces 108 may further includecontrol surfaces, such as trailing edge flaps 112 and/or trim tabs. Tothat end, the canard surfaces 104 and tail surfaces 108 may employ trimtabs to control the trim of the controls to thereby counteractaerodynamic forces and stabilize the VTOL aircraft 100 without the needfor the operator to constantly apply a control force. For example, anelevator may be provided on the aft tail surfaces 108 and ailerons onthe primary wings 106. The trailing edge flaps 112 may be coupled withthe canard, primary, and tail surfaces 104, 106, 108 in accordance withone of more flap configurations, including, for example, plain flaps,slotted flaps, and fowler flaps. While the VTOL aircraft 100 isdescribed as having three lifting surfaces, one of skill in the artwould recognize in view of the subject disclosure that additionallifting surfaces may be employed.

Thrust Rotor 110.

The thrust rotor(s) 110 may employ a wet engine (e.g., a gas turbineengine) and/or an electric motor to produce thrust with a force vectoracting in the horizontal direction. For example, the thrust rotor 110may include a propeller 110 a (e.g., a central hub with a plurality ofrotor blades radiating therefrom) that is driven by a mechanical device,such as an engine or an electric motor (i.e., an electrically-drivenpropeller). The propeller 110 a may include, for example, 4 to 10 rotorblades, or, as illustrated, 6 rotor blades. The propeller 110 a may beconfigured in a pusher propeller configuration (as illustrated) or in atractor configuration. In a tractor configuration, the propeller issituated forward (at the front) of the fuselage 102. During operation,the thrust rotor 110 may be throttled (e.g., under control of the pilotor flight control system) to produce a desired thrust force acting inthe horizontal direction.

Lower Airframe Portion 100 b.

As illustrated, the lower airframe portion 100 b generally comprises aset of substantially parallel rotor booms 118, a set of verticalstabilizers 120, a horizontal stabilizer 122, and a plurality of liftrotors 124 to produce a lifting thrust with force acting in the verticaldirection. In certain aspects, the lower airframe portion 100 b mayfurther comprise a set of auxiliary rotor booms 128. While the verticalstabilizers 120 are illustrated as vertical (and parallel to oneanother), other configurations are possible.

Rotor Booms.

The rotor booms 118 provide a mounting structure for the lift rotors124, where the structural support afforded by the three attachmentpoints provide rigidity and structural weight efficiency (e.g., via thethree attachment points to the canard, wing, and tail lifting surfaces104, 106, 108). As illustrated, a rotor boom 118 may be positioned oneach side of the fuselage 102 to support one or more lift rotors 124 andto support to the upper airframe portion 100 a. The rotor booms 118 maybe substantially parallel to one another and parallel to the lengthwiseaxis (roll axis) of the fuselage 102. The rotor booms 118 may bepositioned below a plane defined by the lower surface of the fuselage102. In certain aspects the rotor booms 118 and lift rotors 124 may bearranged to avoid overlap with the fuselage 102, thereby mitigatedthrust loss. To that end, the lateral distance between the rotor booms118 and the fuselage 102 of the VTOL aircraft 100 may be at least thelength of the rotor blades. In other aspects, the rotor booms 118 may bepositioned closer to the fuselage 102 such that the distal ends of therotor blades of the propeller 124 a extend under the fuselage 102 suchthat they partially overlap with the fuselage 102 during rotation.

A three-point attachment arrangement provides significant structuraladvantages that reduce the overall airframe weight and thus improvesflight efficiency. As illustrated, each rotor boom 118 is coupled to acanard surface 104 and a primary wing 106 of the upper airframe portion100 a, while the rotor boom 118 is coupled to the tail surface 108 viathe horizontal stabilizer 122 (or other cross-member structure tobridge/link the rotor booms 118). Specifically, the canard surfaces 104and tail surfaces 108 may be coupled to, or formed by, the fuselage 102and angled downward (anhedral) towards the rotor booms 118, therebyconnecting the rotor booms 118 with the fuselage 102. This configurationallows for the rotor booms 118 and the lift rotors 124 to be positionedbelow the primary wing 106. The mounting arrangement of the lift rotors124 on the rotor booms 118, between and in the same plane as the liftingsurfaces 104, 106, 108, minimizes rotor-wing interference during thetransition between vertical flight and cruise flight.

Coupling each rotor boom 118 to the upper airframe portion 100 a (e.g.,the fuselage 102) at three (or more) spaced locations (e.g., via liftingsurfaces 104, 106, 108) provides optimum structural stiffness and massdistribution, such that there is less vibration and higher aeroelasticstability. The structural efficiency afforded by the three-pointattachment also reduces the size required for the primary and auxiliaryrotor booms 118, 128, thereby decreasing drag and weight. Accordingly,the width of the rotor booms 118 should be minimized to avoidobstructing airflow from the lift rotors 124 during vertical flight,which will also greatly reduce noise generated by the airflow beingreflected off the rotor booms 118.

As illustrated, for example, each rotor boom 118 can be directly orindirectly coupled to, or supported by, the upper airframe portion 100 aat (or near) rotor boom's 118 distal ends and at a third pointpositioned therebetween. In certain aspects, the three spaced attachmentlocations on the rotor boom 118 may be equidistant. Other configurationsare contemplated, however. For example, the rotor boom 118 may coupledirectly to the tail surface 108 without using the horizontal stabilizer122 or other cross-member structure. Depending on the vertical distancebetween each rotor boom 118 and an attachment point (e.g., of theprimary wing 106), one or more wing support structures 130 may beemployed to bridge the gap, such as cabane struts, pylon(s) orpedestal(s). The one or more wing support structures 130 may beintegrated with the rotor boom 118.

Each rotor boom 118 may further comprise two or more wheels (e.g., afixed wheel 126 a and a steerable wheel 126 b); at least one wheel oneach rotor boom 118 is preferably a steerable wheel 126 b. In certainaspects, the rotor boom 118 may function as pontoons or floats to enabletaking off and landing on water. To that end, the rotor booms 118 may beconfigured as airtight hollow structures to provide buoyancy to the VTOLaircraft 100 in water. The two or more wheels may be powered by a motor,such as an electric motor.

Rotor Disc Area.

The rotor boom 118 facilitates an increased number of lift rotors 124,thereby providing a large disc area to reduce noise, hover power, andenergy use. As illustrated, for example, each rotor boom 118 may supportfour lift rotors 124, each lift rotor 124 having the same diameter.Alternatively, the rotor boom 118 may be extended to accommodateadditional lift rotors 124 of the same diameter. The lift rotors 124 maybe sized to meet a particular need. The rotor boom 118 may be sized toemploy 2 to 10, more preferably 3 to 6, most preferably 4 lift rotors124. For example, a VTOL aircraft 100 configured to transport 2 to 4passengers may employ four 58-inch diameter lift rotors 124 on eachrotor boom 118.

In certain aspects, the lift rotors 124 may employ counter-rotationordering. In order to more closely position the lift rotors 124 on therotor boom 118, thereby increasing the number of lift rotors 124 on agiven length, the sweep of the lift rotor's 124 rotor blades mayoverlap. Except in embodiments where variable speed or counter rotatingrotors are employed, this may be accomplished by meshing the rotorblades such that adjacent rotor blades are out of phase by, for example,90 degrees relative to one another (when 2 bladed propellers are used).Alternatively, the lift rotors 124 may be tilted or offset. Forinstance, the lift rotors 124 may be tilted by a predetermined angle(forward or aft).

The disc area can be further increased (reduces the disc loading) byadding a second set of booms on each side of the fuselage 102.Accordingly, as illustrated in FIGS. 3a and 3b , a set of auxiliaryrotor booms 128 may be employed to provide additional thrust byproviding the physical space (e.g., additional rotor attachment points)needed for additional lift rotors 124. The auxiliary rotor booms 128 maybe coupled to the primary wings 106 and positioned substantiallyparallel to one another and/or to the lengthwise axis (roll axis) of thefuselage 102.

As illustrated, the auxiliary rotor booms 128 are positioned outboardrelative to the rotor booms 118 (e.g., further away from the roll axisthan the “primary” rotor booms 118). The construction of the auxiliaryrotor booms 128 is substantially the same as the rotor booms 118, butthe size (e.g., length) may be adjusted depending on the desired thrustand aircraft footprint. For example, as illustrated, each auxiliaryrotor boom 128 may be sized to mount two additional lift rotors 124 tothe VTOL aircraft 100; however, as with the rotor booms 118, theauxiliary rotor booms 128 may be sized or configured to accommodateadditional (or fewer) lift rotors 124.

A large number of lift rotors 124 (e.g., about 4 to 16 lift rotors 124,most preferably, about 8 to 12 lift rotors 124) creates a large discarea that reduces the noise output of the design and reduces hover powerrequirements. In certain aspects, additional auxiliary rotor booms maybe provided, which may be aligned with (and parallel to) the first setof auxiliary rotor booms 128 or extending forward (or aft) of thefuselage 102.

Empennage.

The set of vertical stabilizers 120 are positioned substantiallyperpendicular to the horizontal stabilizer 122 to define a twin tail(H-tail arrangement or U-tail arrangement) empennage. The horizontalstabilizer 122 may be positioned between (and substantiallyperpendicular to) said rotor booms 118. While the ends of the horizontalstabilizer 122 are illustrated as coupled to the rotor booms 118, thehorizontal stabilizer 122 may be configured to extend beyond the rotorbooms 118. The horizontal stabilizer 122 can function as an attachmentpoint/interface between the upper and the lower airframe portions 100 a,100 b. As illustrated, for example, the

-tail surfaces 108 of the upper airframe portion 100 a can be coupled tothe horizontal stabilizer 122 to provide a combination H- and

-tail arrangement. An example combination H- and

-tail arrangement 400 is illustrated in FIG. 4, where the canard surface104, the primary wing 106, and thrust rotor 110 are omitted to betterillustrate the combination H- and

-tail arrangement 400. As illustrated, the tail surfaces 108 define the

-tail portion of the tail arrangement, while the horizontal stabilizer122 and the vertical stabilizers 120 define the H-tail (or U-tail)portion of the tail arrangement. The existence of an H- or U-tail isdictated by the amount of the vertical stabilizer 120 that extends belowthe horizontal stabilizer 122.

The vertical stabilizers 120 and the horizontal stabilizer 122 mayfurther comprise one of more control surfaces. For example, each of thevertical stabilizers 120 may include a fixed front section and a movablerudder 132 to direct the nose of the VTOL aircraft 100. The horizontalstabilizer 122 may further comprise one or more trailing edge flaps 112and/or trim tabs. The trailing edge flaps 112 may be coupled with thehorizontal stabilizer 122 in accordance with one of more flapconfigurations, including, for example, plain flaps, slotted flaps, andfowler flaps.

While the vertical stabilizers 120 and the horizontal stabilizer 122 arearranged to provide a twin tail empennage, other configurations arecontemplated, including a “T-”, “Pi-”/“π-”, “X-”, “V-”, and “

-” arrangements. In certain aspects, one or more of the verticalstabilizers 120 and the horizontal stabilizer 122 may be all movingand/or fuselage- or wing-mounted.

Lift Rotors 124.

Each lift rotors 124 includes a propeller 124 a driven by a mechanicaldevice, such as an electric motor. The lift rotors 124 are coupled tothe rotor boom 118 with an axis of rotation that is fixed andsubstantially vertical. As illustrated in FIG. 1g , however, each of thelift rotors 124 may be tilted and arranged on the rotor boom 118 suchthat each of the propellers generate a thrust having a substantiallyvertical vector that is directed away from the fuselage 102 (e.g.,directions A₁ and A₂, which are about 5 to 15 degrees outward from thevertical axis). Tilting the lift rotors 124 to generate thrust vectorsthat are directed away (outward) from the fuselage 102 provides forincreased stability during vertical flight. In addition, tilting thelift rotors 124 provides a horizontal component to lift thrust vector,which can be used to control yaw of the VTOL aircraft 100. The spindirection of the lift rotors 124 may further be configured such thatmotor torque changes produce a yaw moment in the same direction.Moreover, as illustrated, the tilting angle defines a rotor plane thatpasses entirely below the fuselage 102, which reduces noise and improvessafety in the event a lift rotor 124 fails and ejects a rotor blade.

To increase efficiency, the lift rotors 124 may be powered only whennecessary (e.g., during the vertical portion of the flightprofile—vertical flight and a portion of transition flight), after whichthe lift rotors 124 may be shut off. While not required for this design,the propeller may further employ variable pitch rotor blades where bladepitch may be controlled, for example, by a swashplate connected to theflight controller 210.

The lift rotors 124 may be designed for low noise during vertical,transition, and cruise flight. The shape and profile of theblades/propellers used for the lift rotors 124 may be designed for lownoise during operation (e.g., during vertical flight). For example, thepropeller may consist of two rotor blades to provide a high degree ofefficiency and low imbalance. The lift rotors 124 may be designed withlow drag characteristics to yield a very low drag penalty, therebyobviating any need to fold or stow the lift rotors 124 or propellers 124a within a rotor boom 118.

When not in use, the propellers 124 a may be arranged in a stowedconfiguration where the rotor blades are parallel to theairflow/airstream, thereby minimizing drag during forward flight.Specifically, the rotors may be secured in an orientation that minimizesthe air resistance and drag of the rotor blades during cruise flight. Inother words, each rotor blade may be positioned in a fore and aftarrangement such that its longitudinal length is parallel to thelongitudinal length (roll axis) of the fuselage 102. FIG. 5 illustratesa lift rotor 124 stowed in an example fore and aft arrangement 500relative to the rotor boom 118, 128. For example, when a propeller withtwo rotor blades is used, the propeller can be arrested and arrangedwith the rotor blades aligned fore and aft, and thus parallel with thefuselage 102 (and the rotor booms 118, 128). In certain aspects, uponreaching cruise flight (or upon reaching a predetermined air speed), thepropellers 124 a may be automatically arrested and arranged in a foreand aft arrangement and/or stowed configuration.

As one of skill in the art would appreciate, the VTOL aircraft 100 canbe scaled up, or down to facilitate a particular purpose based on, forexample, flight objective and/or flight plan. Moreover, while the VTOLaircraft 100 is described as having a thrust rotor 110 and lift rotors124 that employ electrically-driven propellers 124 a, various propulsiontypes are contemplated. In certain aspects, the VTOL aircraft 100 is anall-electric aircraft, whereby a rechargeable battery bank (e.g., viabattery system 212) is used to power one or more electric motors togenerate thrust. In another aspect, the VTOL aircraft 100 may be ahybrid aircraft where a wet engine (e.g., a gas turbine engine) is usedto generate electricity (via a generator) to power one or more electricmotors to generate thrust, in which case a battery bank is provided tostore power from the generator. In yet another aspect, the VTOL aircraftuses a hybrid of turbine and electric thrusting. For example, a primaryengine may be configured as the thrust rotor to produce thrust forforward flight, while electrically-driven fans are used to generatelift. An example hybrid turbine electric thrusting system is describedby commonly owned U.S. Pat. No. 7,857,254 to Robert Parks, entitled“System and Method for Utilizing Stored Electrical Energy for VTOLAircraft Thrust Enhancement and Attitude Control.”

The above-cited patents and patent publications are hereby incorporatedby reference in their entirety. Although various embodiments have beendescribed with reference to a particular arrangement of parts, features,and like, these are not intended to exhaust all possible arrangements orfeatures, and indeed many other embodiments, modifications, andvariations can be ascertainable to those of skill in the art. Thus, itis to be understood that the invention may therefore be practicedotherwise than as specifically described above.

What is claimed is:
 1. A vertical take-off and landing (VTOL) aircraftcomprising: a fuselage having a roll axis; a thrust rotor to produce apropulsion thrust; first and second rotor booms, wherein the first andsecond rotor booms are substantially parallel to the roll axis of thefuselage, and the fuselage is positioned between the first and secondrotor booms; first and second canard surfaces, each of said first andsecond canard surfaces having a canard proximal end and a canard distalend, wherein the canard proximal end of the first canard surface iscoupled to the fuselage and the canard distal end of the first canardsurface is coupled to the first rotor boom, wherein the canard proximalend of the second canard surface is coupled to the fuselage and thecanard distal end of the second canard surface is coupled to the secondrotor boom; first and second wing surfaces, each of said first andsecond wing surfaces having a wing proximal end and a wing distal end,wherein the wing proximal end of each of the first wing surface andsecond wing surface is coupled to the fuselage, wherein the first wingsurface is coupled to the first rotor boom and the second wing surfaceis coupled to the second rotor boom; a cross-member structure having afirst cross-member end and a second cross-member end, wherein the firstcross-member end is coupled to the first rotor boom and the secondcross-member end is coupled to the second rotor boom; first and secondtail surfaces, each of said first and second tail surfaces having a tailproximal end and a tail distal end, wherein the tail proximal end of thefirst tail surface is coupled to the fuselage and the tail distal end ofthe first tail surface is coupled to the cross-member structure, whereinthe tail proximal end of the second tail surface is coupled to thefuselage and the tail distal end of the second tail surface is coupledto the cross-member structure; a first plurality of lift rotorspositioned on the first rotor boom to produce a first lifting thrustforce; and a second plurality of lift rotors positioned on the secondrotor boom to produce a second lifting thrust force.
 2. The VTOLaircraft of claim 1, wherein the cross-member structure defines a lengththat is substantially perpendicular to the said first and second rotorbooms.
 3. The VTOL aircraft of claim 1, wherein the cross-memberstructure is positioned aft of said first and second wing surfaces. 4.The VTOL aircraft of claim 1, wherein the first and second tail surfacesare configured at anhedral angles.
 5. The VTOL aircraft of claim 1,wherein the first and second plurality of lift rotors are automaticallyarranged in a stowed configuration during cruise flight.
 6. The VTOLaircraft of claim 1, wherein the first plurality of lift rotors consistsof four lift rotors and the second plurality of lift rotors consists offour lift rotors.
 7. The VTOL aircraft of claim 1, wherein each of thefirst and second plurality of lift rotors is tilted such that each ofthe first and second lifting thrust forces is directed outward from thefuselage.
 8. The VTOL aircraft of claim 1, wherein the thrust rotor iscoupled to the fuselage.
 9. The VTOL aircraft of claim 1, wherein thethrust rotor is configured in a pusher propeller configuration.
 10. TheVTOL aircraft of claim 1, wherein the first and second canard surfacesand the first and second tail surfaces are configured at anhedralangles.
 11. The VTOL aircraft of claim 10, wherein the first and secondwing surfaces are configured at dihedral angles.
 12. The VTOL aircraftof claim 1, wherein each of the first plurality of lift rotors and thesecond plurality of lift rotors employs a propeller consisting of tworotor blades.
 13. The VTOL aircraft of claim 12, wherein the propelleris arranged with the two rotor blades aligned fore and aft when in astowed configuration.
 14. The VTOL aircraft of claim 1, wherein each ofthe first and second plurality of lift rotors include a propeller drivenby an electric motor.
 15. The VTOL aircraft of claim 14, wherein thethrust rotor includes a propeller driven by an electric motor.
 16. TheVTOL aircraft of claim 1, wherein the cross-member structure is ahorizontal stabilizer.
 17. The VTOL aircraft of claim 16, wherein saidfirst rotor boom comprises a first vertical stabilizer and said secondrotor boom comprises a second vertical stabilizer.
 18. The VTOL aircraftof claim 17, wherein a first end of the horizontal stabilizer is coupledto the first vertical stabilizer and a second end of the horizontalstabilizer is coupled to the second vertical stabilizer.
 19. The VTOLaircraft of claim 1, comprising third and fourth rotor booms, whereinthe third and fourth rotor booms are substantially parallel to the rollaxis of the fuselage and outboard relative to the first and second rotorbooms.
 20. The VTOL aircraft of claim 19, wherein the third rotor boomis coupled to the first wing surface and the fourth rotor boom iscoupled to the second wing surface.
 21. The VTOL aircraft of claim 19,wherein the third rotor boom comprises a third plurality of lift rotorsand the fourth rotor boom comprises a fourth plurality of lift rotors.22. The VTOL aircraft of claim 21, wherein the third plurality of liftrotors consists of two lift rotors and the fourth plurality of liftrotors consists of two lift rotors.
 23. A vertical take-off and landing(VTOL) aircraft comprising: a fuselage defining a roll axis; a thrustrotor to produce a propulsion thrust; first and second rotor booms,wherein the first and second rotor booms are substantially parallel tothe roll axis of the fuselage, and the fuselage is positioned betweenthe first and second rotor booms; first and second canard surfaces, eachof said first and second canard surfaces having a canard proximal endand a canard distal end, wherein the canard proximal end of the firstcanard surface is coupled to the fuselage and the canard distal end ofthe first canard surface is coupled to the first rotor boom, wherein thecanard proximal end of the second canard surface is coupled to thefuselage and the canard distal end of the second canard surface iscoupled to the second rotor boom; first and second wing surfaces, eachof said first and second wing surfaces having a wing proximal end and awing distal end, wherein the wing proximal end of each of the first wingsurface and second wing surface is coupled to the fuselage, wherein thefirst wing surface is coupled to the first rotor boom and the secondwing surface is coupled to the second rotor boom; first and second tailsurfaces, each of said first and second tail surfaces having a tailproximal end and a tail distal end, wherein the tail proximal end of thefirst tail surface is coupled to the fuselage and the tail distal end ofthe first tail surface is coupled to the first rotor boom, wherein thetail proximal end of the second tail surface is coupled to the fuselageand the tail distal end of the second tail surface is coupled to thesecond rotor boom; a first plurality of lift rotors positioned on thefirst rotor boom to produce a first lifting thrust force; and a secondplurality of lift rotors positioned on the second rotor boom to producea second lifting thrust force, wherein each of the first and secondplurality of lift rotors is tilted such that each of the first andsecond lifting thrust forces is directed outward from the fuselage.